Today, most whole blood collected from donors is not itself stored and used for transfusion. Instead, the whole blood is separated into its clinically proven components (typically red blood cells, platelets, and plasma), which are themselves individually stored and used to treat a multiplicity of specific conditions and diseased states. For example, the red blood cell component is used to treat anemia; the concentrated platelet component is used to control thrombocytopenic bleeding; and the platelet-poor plasma component is used as a volume expander or as a source of Clotting Factor VIII for the treatment of hemophilia.
Systems composed of multiple, interconnected plastic bags have met widespread use and acceptance in manually collecting these blood components for storage. A typical manual collection procedure collects 450 ml of whole blood from a donor in a primary bag. The donor departs, and the primary bag is centrifuged to separate the whole blood into plasma and red blood cells. For a typical donor, the manual collection procedure yields about 250 ml of concentrated red blood cells and about 200 ml of plasma, which are each expressed from the primary bag into individual storage bags. A majority of the platelets reside either with the plasma or with the red blood cells, depending upon the amount of centrifugal force exerted. Leukocytes typically reside primarily with the red blood cells. These leukocytes can be removed by filtration either before or after storage and prior to transfusion.
Manual collection procedures typically produce relatively high concentrations of red blood cells, which typically have hematocrits after centrifugal separation of about 70% to 80%. Hematocrit expresses the percentage volume of red blood cells to whole, or total, blood volume. In comparison, the hematocrit of whole blood for a typical healthy donor before centrifugation is about 40% to 45%, although whole blood hematocrits do vary significantly among donors from the 30 percentile range into the 50 percentile range. In the United States, federal regulations prohibit individuals with whole blood hematocrits of 38% and below from donating blood.
In the United States, federal regulations also prohibit collecting more than 250 ml of red blood cells from an individual donor during a given collection procedure. These federal regulations further require a six week interval between red blood cell collections.
Manual and automated blood collection procedures, called plasmapheresis, have been developed for collecting increased volumes of plasma from an individual donor at more frequent intervals. During plasmapheresis, red blood cells are returned to the donor, so that greater total volumes of whole blood can be processed. The result is greater total volumes of plasma collected, which typically range between 400-450 ml (for manual plasmapheresis) up to 880 ml (for automated plasmapheresis procedures).
Fischel U.S. Pat. No. 5,034,135, entitled "Blood Fractionation System and Method," discloses a membrane separation device widely used today for performing automated plasmapheresis. The device employs a rotating microporous membrane to separate whole blood into platelet poor plasma, which is retained, and concentrated red blood cells, which are returned to the donor. Prince et al. U.S. Pat. Nos. 4,879,040 and 5,069,792 describe control systems for optimizing plasma flow using the rotating membrane device, based in part upon monitoring transmembrane pressure.
While very effective in optimizing the collection of plasma, these control systems, as implemented in the Prince et al. '040 and '792 Patents, are not practically adapted for the collection of red blood cells for storage. This is because, as implemented in the Prince et al. '040 and '792 Patents, the hematocrit of the concentrated red blood cell collected is highly dependent upon the whole blood hematocrit of the donor. That is, the hematocrit of the concentrated red blood cell output for a low hematocrit donor will be lower than the hematocrit of the concentrated red blood cell output for a high hematocrit donor.
The need still exists for systems and methods that marry the collection of red blood cells in uniformly high concentrations, comparable to those of centrifugal whole blood separation procedures, with the collection of plasma in increased volume amounts comparable to those of at least manual plasmapheresis procedures. The need particularly exists for such systems and methods that can achieve these objectives uniformly for all donors, including those having relatively low whole blood hematocrits. The need is further intensified for systems that can accomplish low cost, efficient red blood cell collection on a par with manual systems, but in an automated fashion.